Nowadays, global positioning systems (GPS) are widely used in many applications including vehicle applications and mobile electronic applications to provide an absolute position for a moving object according to satellite signals. A time to first fix (TTFF) parameter is an important parameter to evaluate the performance of the GPS. The TTFF parameter means the time to first fix the moving object after a GPS receiver starts. Generally, users want to fix the current position of the moving object in a shorter time after starting the GPS receiver.
The GPS receiver operates in several modes that include a cold starting mode, a warm starting mode and a hot starting mode according to different prior information stored in the GPS receiver. Generally, the GPS receiver operates in the cold starting mode when the GPS receiver starts to work. The cold starting mode means the GPS receiver starts in the condition with no prior information (e.g., satellite ephemeris, satellite almanac, prior position of the GPS receiver, clock information and etc.) stored in the GPS receiver.
FIG. 1 illustrates a flowchart 100 of operations performed by a conventional GPS receiver in the cold starting mode. As shown in FIG. 1, when the GPS receiver starts in the cold starting mode, the GPS receiver can acquire all the satellite signals in block 102, track the available satellite signals in block 104, capture the C/A codes from each of the satellite signals in block 106, demodulate the C/A codes to recover the navigation bits in block 108, synchronize navigation data subframe based on the navigation bits in block 110, gather satellite ephemeris in block 112, and fix a current position in block 114.
During the operation, the GPS receiver determines a first boundary of the navigation bits after receiving multiple C/A codes, and then starting from the boundary, demodulates the C/A codes to recover the navigation bits after the first boundary. Therefore, the navigation bits before the first boundary are not exploited because the C/A codes before the first boundary are not used but discarded. However, an enough number of navigation bits should be recovered in order to calculate the current position. As a result, the GPS receiver has to spend a relatively long time to recover the navigation bits after the first boundary for calculating the position. Therefore, it is to a GPS receiver system for fast recovery of the navigation bits that this invention is primarily directed.